1. Field of the Invention
The present invention relates to a battery electrode produced by bonding a lead to a three-dimensional porous metal body and a manufacturing method and apparatus for the same.
2. Description of the Related Art
A battery electrode usually includes a lead to be connected to a positive electrode terminal or a current collecting plate. This type of battery electrode has been manufactured by a resistance seam welding process. Specifically, as shown in FIG. 6, first, a rod-shaped Cu electrode 22 for welding is brought into contact with a lead 21, which has been laid on top of a three-dimensional porous metal body 20. Then, the lead 21 is pressed into close contact with the three-dimensional porous metal body 20, and a large amount of current flows between the three-dimensional porous metal body 20, acting as a positive electrode, and the Cu electrode 22, acting as a negative electrode. Thus, the lead 21 is spot-welded to the three-dimensional porous metal body 20. Then, the three-dimensional porous metal body 20, to which the lead 21 has been welded, is filled with an active material and rolled. Finally, the three-dimensional porous metal body 20 thus filled with an active material and rolled is cut to a predetermined size, resulting in a battery electrode.
However, the method for manufacturing a battery electrode by the resistance seam welding process makes continuous production difficult and increases the running cost. This is because the lifetime of the Cu electrode 22 for welding is short, which requires maintenance at frequent intervals. Moreover, when the Cu electrode 22 is used as a welding electrode, though the welding performance is improved, sputtering occurs to increase short-circuits because of the inclusion of Cu. In addition, the active material that enters the gap between the lead 21 and the three-dimensional porous metal body 20 during the filling process remains, so that faulty welding often is caused when the battery electrode and a current collecting plate are welded together, and short-circuits are increased as well.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a battery electrode that can be produced continuously at a lower running cost, reduce the faulty welding with a current collecting plate, and prevent short-circuits, and a manufacturing method and apparatus for the same.
To achieve the above object, a configuration of a battery electrode of the present invention includes an electrode plate and a lead bonded to the electrode plate. The entire surface of the lead opposed to the electrode plate is bonded ultrasonically to the electrode plate. This configuration can provide a battery electrode to which the entire surface of the lead opposed to the electrode plate is bonded, so that no active material enters the bonding area between the lead and the electrode plate. When the electrode is cut to a predetermined size, the lead also is cut. Therefore, if any active material has entered the bonding area, the material comes out during cutting. This is likely to cause the faulty welding between the electrode and a current collecting plate. However, the configuration of a battery electrode of the present invention is such that no active material enters the bonding area between the lead and the electrode plate, so that the faulty welding can be reduced.
In the configuration of a battery electrode of the present invention, it is preferable that the electrode plate is a three-dimensional porous metal body, and that the lead is bonded to one edge portion of the three-dimensional porous metal body.
In the configuration of a battery electrode of the present invention, it is preferable that the entire surface of the electrode plate is patterned by applying pressure, to which the lead is bonded. Those patterns can be used to judge whether the bonding strength is optimized or whether the uniformity of bonding is maintained over the lead surface.
A method for manufacturing a battery electrode of the present invention includes bonding a lead to an electrode plate. In this method for manufacturing a battery electrode, a three-dimensional porous metal body is used as the electrode plate, and the lead is continuously bonded ultrasonically to the three-dimensional porous metal body, which then is filled with an active material and rolled. According to this method for manufacturing a battery electrode, the entire surface of the lead opposed to the three-dimensional porous metal body can be bonded continuously thereto. As a result, no active material enters the bonding area between the three-dimensional porous metal body and the lead during the filling and rolling processes. Thus, the faulty welding between the electrode and a current collecting plate can be reduced.
In the method for manufacturing a battery electrode of the present invention, it is preferable that any excess active material is removed after the filling and rolling processes. According to this preferred example, the excess active material that adheres to the lead portion and the surface of the three-dimensional porous metal body can be removed. Therefore, the faulty welding between the final battery electrode and a current collecting plate can be reduced, and short-circuits can be prevented as well. In this case, the excess active material is removed preferably by spraying air. According to this preferred example, the excess active material can be removed easily. Also, the same effect can be obtained by brushing. In this case, it is further preferable that the removed excess active material is collected by suction.
An apparatus for manufacturing a battery electrode of the present invention includes an ultrasonic horn and an anvil. The ultrasonic horn is in the form of a disk, and can rotate around a central axis and vibrate in the central axis direction. The anvil is in the form of a disk, arranged opposing the ultrasonic horn on the same plane, and can rotate around a central axis. The ultrasonic horn and the anvil move relative to each other so that the circumferential surfaces of the ultrasonic horn and the anvil can be pressed together to make contact continuously. The apparatus for manufacturing a battery electrode having the above configuration is provided with the disk-shaped ultrasonic horn and anvil. Therefore, a hoop material can be used as a workpiece, i.e., the material to be welded is supplied continuously from a roll. As a result, battery electrodes can be produced continuously by supplying the hoop material, thereby reducing the running cost.
In the configuration of the apparatus for manufacturing a battery electrode of the present invention, it is preferable that the anvil has concavities and convexities formed on the circumferential surface thereof. According to this preferred example, the function of holding a workpiece can be enhanced. In this case, it is preferable that the surface area of the convexities is 10% to 50% of the overall occupied area of the circumferential surface of the anvil. Also, in this case, it is preferable that the circumferential surface of the anvil is coated with ceramic or plated with nickel. Moreover, in this case, a depth of the concavities preferably is in the range of 20 xcexcm to 100 xcexcm.
In the configuration of the apparatus for manufacturing a battery electrode of the present invention, it is preferable that the ultrasonic horn has a flat circumferential surface. This preferred example can improve the maintenance of the ultrasonic horn and increase the lifetime thereof, so that the efficiency of the continuous production of battery electrodes is improved.
In the configuration of the apparatus for manufacturing a battery electrode of the present invention, it is preferable that a width of the circumferential surface of the ultrasonic horn is the same as that of the anvil, and that both edges of the circumferential surfaces of the ultrasonic horn and the anvil are cut off. According to this preferred example, since the abrasion of the ultrasonic horn and the anvil proceeds simultaneously, the lifetime of the apparatus can be made still longer. Moreover, this preferred example can prevent the vicinity of the lead portion from being cut when the lead portion of the workpiece is pressed between the ultrasonic horn and the anvil.
As described above, the present invention can provide a battery electrode that can be produced continuously at a lower running cost, reduce the faulty welding with a current collecting plate, and prevent short-circuits.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.